Particle Selection in Suspension-Feeding Bivalves: Does One Model Fit All?

Suspension-feeding bivalves are known to discriminate among a complex mixture of particles present in their environments. The exact mechanism that allows bivalves to ingest some particles and reject others as pseudofeces has yet to be fully elucidated. Recent studies have shown that interactions between lectins found in the mucus covering oyster and mussel feeding organs and carbohydrates found on the microalga cell surface play a central role in this selection process. In this study, we evaluated whether these interactions are also involved in food selection in bivalves with other gill architectures, namely, the clam Mercenaria mercenaria and the scallop Argopecten irradians. Statistical methods were used to predict whether given microalgae would be rejected or ingested depending on their cell surface carbohydrate profiles. Eight different microalgae with previously established surface carbohydrate profiles were grown and harvested during their exponential growth phase to be used in feeding experiments. Microalgae were then used in 17 feeding experiments where different pairs of microalgae were presented to clams and scallops to evaluate selection. Decision trees that model selection were then developed for each bivalve. Results showed that microalgae rich in mannose residues were likely to be ingested in both bivalves. N-acetylglucosamine and fucose residues also seem to play a role in food particle choice in scallops and clams, respectively. Overall, this study demonstrates the role of carbohydrate-lectin interactions in particle selection in suspension-feeding bivalves displaying different gill architectures, and it highlights the importance of mannose residues as a cue for the selection of ingested particles.